1. Field of the Invention
This invention relates to a steering wheel provided with a luminous (light-emitting) display device, and more particularly to a steering wheel having a luminous display device mounted on a pad portion or other portion of the steering wheel of a vehicle so as to display operating conditions of various devices by way of predetermined characters or signs.
2. Description of the Prior Art
In conventional steering wheels of the type described, there have been adopted various countermeasures against the situation in which light from a luminous display device is reflected in a front window of a vehicle, thereby hindering the driving of the vehicle. For example, in Japanese Utility Model Unexamined Publication No. 57-120166, there is proposed a steering wheel of the type where a luminous display device is covered with a light-intercepting cover member so as to prevent the light from being reflected by a front window. There is further proposed a steering wheel of the type a luminous display device is mounted deep in a hole formed in a pad portion of the steering wheel, in order to prevent the dissipation of the light from the luminous display device, thereby preventing the light from being reflected in the front window.
However, the former steering wheel utilizing the light-intercepting cover member has a problem where the light-intercepting cover member is projected beyond the surface of the pad portion, thus detracting from the appearance of the steering wheel. Another problem of the steering wheel with the light intercepting cover member is that the number of component parts is increased because of the light-intercepting cover member.
In the steering wheel having the luminous display device mounted in the hole in the pad portion, the pad portion must have a considerable thickness to accommodate this construction, thus resulting in a problem that the steering wheel is disposed closer to the driver. To overcome this difficulty, it is necessary to extensively modify the design of a steering column portion so as to adjust the position of the steering wheel.
One example of conventional luminous display device used in a steering wheel is shown in FIG. 7. This luminous display device is mounted on a flat portion of a pad portion 2 of the steering wheel. In FIG. 7, the upper side represents the upper surface side of the pad portion 2, and the lower side represents the interior side of the pad portion 2. A through hole 23a is formed through the pad portion 2, and a lamp unit 30 is mounted in the through hole 3 from the inner side of the pad portion 2. The lamp unit 30 has a reflection chamber 9 open to the through hole 23a of the pad portion 2. A display lamp 15 is mounted on one side of the reflection chamber 9. A bottom wall 9b of the reflection chamber 9 is inclined, and defines a reflection surface 11. A flat dissipation plate 31 is mounted within the through hole 3, and closes the opening of the reflection chamber 9. A transparent character plate 6 is mounted on the upper surface of the pad portion 2 via a printing layer 18. Printing is not applied to predetermined character portions of the printing layer 18 through which the light emitted from the display lamp 15 is transmitted. The light emitted from the display lamp 15 is reflected by the reflection surface 11, so that the direction of travel of the light is changed, and then the reflected light transmits through and is dissipated by the dissipation plate 31. Then, the dissipated light transmits through the transparent portions of the character plate 6. Therefore, the characters are luminously displayed on the character plate 6, thereby transmitting predetermined information to the driver.
A light-emitting diode (LED) 20 is provided within the through hole 23a, and light from the LED 20 does not transmit through the dissipation plate 31 but transmits directly through the transparent portions of the character plate 6, thereby luminously displaying the signs on the character plate 6.
However, when the light from the display lamp 15 is to be reflected by the reflection surface 11 as described above, the light reflected by those portions of the reflection surface Il farther from the display lamp 15 travels along longer paths before reaching the dissipation plate 31. Therefore, the farther the light reflected by the reflection surface 11 is from the display lamp 15, the weaker the light reaching the dissipation plate 31 becomes. Hence, the distribution of the light is uneven, thus resulting in a problem that the luminous conditions of the characters on the character plate 6 become uneven.
Further, since no partition wall is provided between the upper side of the dissipation plate 31 and the LED 20, the light dissipated by the dissipation plate 31 is mixed with the light emitted from the LED 20, so that the display of the characters and signs becomes unclear. Further, in the case where the color tone of the light emitted from the display lamp 15 is different from that of the light emitted from the LED 20, there is encountered the problem that each of the characters and signs cannot be made luminous in a desired color tone because of the mixing of the two lights.